Loss of antinodal coherence with a single d-wave superconducting gap leads to two energy scales for underdoped cuprate superconductors

摘要

We address the question of the two energy scales in the superconducting state of hole-doped copper-oxide superconductors below the optimal doping level. We show by performing temperature-dependent Raman scattering measurements on Bi_2Sr_2CaCu_2O_(8+δ) that the two energy scales often assigned to two distinct gaps, are both associated with coherent Bogoliubov quasiparticles and can be simply explained by a one single d-wave gap and the loss of antinodal coherence. We then establish that the critical temperature T_c is controlled by the fraction of coherent Fermi surface f_c around the nodes such as: k_BT_∝f_c-△_(max), where △_(max) is the maximum amplitude of the superconducting gap.